1. Field of the Invention
The present invention relates to a light absorbent agent polymer useful for organic anti-reflective coatings which can prevent diffused light reflection of the bottom film layer or substrate and reduce standing waves caused by a variation of thickness of the photoresist itself, thereby, increasing uniformity of the photoresist pattern, in a process for forming ultra-fine patterns of photoresist for photolithography by using 193 nm ArF among various processes for manufacturing semiconductor device, and its preparation method.
Also, the present invention provides an organic anti-reflective coating composition (hereinafter abbreviated as “the coating composition”) comprising the light absorbent agent polymer for the organic anti-reflective coating (hereinafter abbreviated as “the coating polymer”) and a pattern formation process using the coating composition.
2. Description of the Related Art
In a fabrication process of ultrafine patterns for preparing semiconductor devices, standing waves and reflective notching inevitably occur due to the optical properties of lower film layer on the photoresist film and due to the thickness changes in the photosensitive film. In addition, there is another problem in that a CD (critical dimension) alteration is caused by diffracted and reflected light from the lower film layers. Thus, it has been suggested to introduce anti-reflective coating that prevents back reflection of a lower film layer between a lower film and a photoresist by introducing organic material with high absorbance at a wavelength range of the light employed as a light source.
Especially, when exposed to UV light from the light source, a photoresist thin film is transmitted by the UV light, thus allowing the light absorbed in bottom portion of the thin film to be scattered and/or reflected. Such an anti-reflective coating can absorb the scattered and/or reflected light and, thereby, directly affecting the fine processing of the photoresist.
Anti-reflective coatings are classified into inorganic and organic anti-reflective coatings depending upon the material used, or as absorptive and interfering anti-reflective coatings based on the operation mechanism. For a fine pattern forming process using I-line (365 nm wavelength) radiation, inorganic anti-reflective coating are predominantly used, while TiN and amorphous carbon (a-C) are employed as an absorptive system anti-reflective coating and SiON are employed as an interfering system anti-reflective coating. In a fabrication process of ultrafine patterns using KrF light (248 nm), an inorganic anti-reflective coating has been mainly used and an organic anti-reflective coating has been used occasionally along with the inorganic anti-reflective coating.
However, in an ultra-fine pattern forming process using ArF light (193 nm), no proper anti-reflective coating has been developed yet. Especially, in the case of an inorganic anti-reflective coating, no material has been known which enables the control of the interference at 193 nm, the wavelength of the light source. Thus, there has been great deal of efforts to employ an organic compound as an anti-reflective coating.
To be a good organic anti-reflective coating, the following conditions must be satisfied.
First, an anti-reflective coating must not be dissolved by a solvent of the photoresist in the process of laminating an anti-reflective coating and then coating photoresist on the top portion thereof. In order to achieve this goal, such an anti-reflective coating must be designed to form a cross-linked structure without producing any chemical by-product, in a process of lamination an anti-reflective coating by coating an anti-reflective coating composition and then performing a baking process.
Second, in order to prevent diffused light reflection from a bottom film layer, the coating must contain certain materials to absorb light at the wavelength range of the exposure light source.
Third, no flowing in and out by chemicals such as acid or amine occur from the anti-reflective coating. This is because when acid migrates from anti-reflective coating to a photoresist film of an unexposed portion, undercutting occurs at a lower part of the pattern while footing may occur when a base, such as amine, migrates to the photoresist film. Such a phenomenon can be stopped by preventing such chemicals from coming in or going out of the anti-reflective coating.
Fourth, the etching speed of the anti-reflective coating should be faster than the etching speed of the upper photosensitive film so as to facilitate an etching process by using photosensitive film as a mask.
Finally, the anti-reflective coating must be as thin as possible to an extent as to sufficiently play a role as an anti-reflective coating.
In order to satisfy the above requirements, conventional organic anti-reflective coating compositions generally comprise a cross-linking agent to allow the anti-reflective coating to have a cross-linked structure, a light-absorbing agent to absorb the light at the wavelength range of exposure light source, a thermal acid generator as a catalyst for activating the cross-linking reaction, and an organic solvent.
As mentioned above, it strongly requires a novel organic anti-reflective coating preferably useable as the anti-reflective coating for the ArF light source at 193 nm, which can control the interference phenomenon to the ArF light source. Therefore, the present inventors have developed an anti-reflective coating polymer capable of controlling the interference phenomenon to the ArF light source, as well as to satisfy all of the requirements mentioned above, and a composition comprising the coating polymer, thereby accomplishing the present invention.